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I understand lactose intolerance (actually the norm for adult mammals). What I don't understand is you particularly signaling out cow's milk. Lactose is a component of all milk.
Checking in Wikipedia (milk) I noted that the four primary types of milk (commercially available throughout the world) are roughly equal in lactose content. (Aside: Human milk is on the notably higher, although lower in fat and thus not that great in coffee . . .)
It might actually be related to what the feed cows (if it is cows-milk specific). Antibiotics,for example, and who knows what else.
I have a relative who's sensitive to casein - still a component of all milk. And a sprinkling of lactose intolerance.
You'd be correct on another (possible) basis: In general, yogurts and cheeses no longer have (significant, if any) lactose content - it's consumed by the bacteria used in the process. It's rather common for lactose-intolerant people to be able to eat these items with no ill effects.